           [unit (take arg (injection-rate-seq unit))])
         (keyword? arg)
         (repeatedly (fn [] (typical-injection-rate arg)))))
-
-(defn rand-proppant-concentration-unit []
-  (rand-nth [:lb-per-gal :lb/gal :kg-per-m3 :kg/m3]))
 
 (defn typical-proppant-concentration
   ([]

(defn typical-fracture-azimuth []
  (tuc/draw-normal 90 30))

(defn rand-length-unit []
  (rand-nth [:ft :m]))

(defn typical-fracture-geometry 
  ([unit] [(map #(vector unit %) (typical-fracture-size unit)) (typical-fracture-azimuth)])
  ([] (typical-fracture-geometry (rand-length-unit))))


                   [:m :ft] #(/ (* % 100) 30.48)}]
    (converter [from to])))

(defn rand-unit [physical-quantity]
  (let [quantity-units-map {:length [:ft :m]
                            :mass [:lb :kg]
                            :pressure [:psi :kPa :mPa]
                            :volume [:bbl :m3]
                            :injection-rate [:bbl-per-min :bpm :m3-per-min :m3/min]
                            :proppant-concentration [:lb-per-gal :lb/gal :kg-per-m3 :kg/m3]}]
    (fn [] (rand-nth (get quantity-units-map physical-quantity)))))

(def rand-length-unit (rand-unit :length))
(def rand-mass-unit (rand-unit :mass))
(def rand-pressure-unit (rand-unit :pressure))
(def rand-volume-unit (rand-unit :volume))
(def rand-injection-rate-unit (rand-unit :injection-rate))
(def rand-proppant-concentration-unit (rand-unit :proppant-concentration))

(defn typical-monitor-pressure
  ([units]
